I got this private message from Ian C,which I found very helpful:

"I’m surprised anyone thinks that 2-bath fixing is controversial. I read the recommendations and the reasons for doing so many years ago in books written by the personnel of Eastman Kodak. I believed then as I do now that they were the most authoritative source of photography materials knowledge. I started darkroom work in 1987. One of my coworkers gave me a single film-developing and printing lesson in his darkroom. He used single-bath fixing. He told me that people who process a greater volume usually use 2-bath fixing, but he didn’t do that. He simply discarded his fixer after 25 8” x 10” prints. It works, provided you’re good at keeping track of the number of prints you’ve fixed and don’t “cheat”. After I’d done this a couple of years, I noticed that some of my older Kodak Polycontrast prints had ugly purplish stains on them. It takes a few years of reaction with the oxygen in the air for this to become evident, but then it’s too late.

I did some reading of Kodak books. The stains matched their descriptions of “inadequate fixing”. Further reading suggested that I could eliminate the problem by 2-bath fixing. I practiced this from that point on and never had another stain-ruined print. You may already know this, but I think it’s worth repeating. In 2-bath fixing, fix 1 does the majority of the work, even if it has become weak. Then bath 2 only has to dissolve any small amount of unexposed silver salts that remain. After 25-30 8” x 10” prints (2000-2400 sq. inch) you scrap fix 1 and the partially used fix 2 becomes the new fix 1. Of course you need a new fix 2. You repeat the process every 2000-2400 sq. inches of processed paper. In this way you always have a relatively strong fix 2 ready to intercept any unexposed silver salts still remaining in the print after fix 1. It’s a clever idea, gives you maximum use of your fixer, and guarantees complete fixing so that you prints are permanent with respect to fixing. I can’t imagine why anyone would do otherwise."